A kinetic method for the determination of organosulfur compounds by inhibition: determination of cysteine, 2,3-dimercaptopropanol and thioglycolic acid

Abstract

A kinetic method for the determination of organosulfur compounds by UV spectrophotometry is described. Organosulfur compounds have been shown to inhibit the Hg(II)-catalyzed substitution of cyanide in hexacyanoferrate(II) by 2-methylpyrazine (2-Mepz). The inhibitory effect is proportional to the concentration of inhibitor and can be used as the basis for the determination of trace amounts of organosulfur compounds such as cysteine, 2,3-dimercaptopropanol (DMP) and thioglycolic acid (TGA). Both the influence of the reaction variables and interference of a variety of ions have been studied. A mechanism for the inhibition process is proposed. The determination range depends on the amount of Hg(II) added and stability of the Hg(II)-ligand complex. Kinetic parameters were determined from Lineweaver-Burk plots, obtained in the absence and presence of the inhibitor. Excellent linearity is observed for all analytes over their respective concentration ranges with correlation coefficient [0.9. The condition calibration curves were linear in the range of 5 9 10 -6 -15 9 10 -6 M for cysteine, 1 9 10 -7 -7 9 10 -7 M for DMP and 1 9 10 -6 -10 9 10 -6 M for TGA. The detection limits were 1.18 9 10 -7 M for cysteine, 4.16 9 10 -8 M for DMP and 1.30 9 10 -7 M for TGA. The effects of amino acids that can interfere in the determination of cysteine were studied.

Surface‐Bonding‐Enhanced Self‐Co‐Reactant Electrogenerated Chemiluminescence for Sensitive and Selective Detection of Thioglycolic Acid in Cosmetics

“…Since TGA is the main ingredient in hair perm agent, its simple and accurate sensing will be welcome. So far many attempts have been made to develop analytical methods for TGA determination, such as, chromatographic method, [6] electrochemical analysis, [7] potentiometry, [8] capillary electrophoresis, [9] spectroscopic method [10] and colorimetry [11] . Some of the methods need sophisticated instrumentations and time‐consuming, and hence, simple, cheap and sensitive detection method for TGA is highly needed.…”